But he was specifically talking about having boost at idle. If there is boost, the BOV is closed. That's how they are designed.
hmm. how come no one ever recommends a 272 to anyone building a 2.8? it would just be common sense to do so, reading on this thread and finding out that even if it were turboed that it would still work.
But he was specifically talking about having boost at idle. If there is boost, the BOV is closed. That's how they are designed.
I was explaining how it's not possible to have boost in the plenum at idle. It is theoretically possible to have boost in the charge pipe at idle; however if that were the case then the BOV would be opened.
A cam with a lot of overlap can be less desirable for boost because you can lose some of the charge straight out the exhaust. I don't know if the 272 has enough overlap to cause this to happen.
I was explaining how it's not possible to have boost in the plenum at idle. It is theoretically possible to have boost in the charge pipe at idle; however if that were the case then the BOV would be opened.
A cam with a lot of overlap can be less desirable for boost because you can lose some of the charge straight out the exhaust. I don't know if the 272 has enough overlap to cause this to happen.
The bov works off crankcase vacuum. Vacuum, When the throttle plate is closed, and no boost is introduced to correct the vacuum.. The vacuum will suck the plunger on the bov, and boost on the charge pipe together will be enough to overpower the bov spring and slightly open. When the throttle plate is open and the motor is under boost, the engine vacuum turns to pressure and forces the bov closed. If the engine was building boost at idle, then it would be forcing the bov closed, and the pressure in the charge pipe would be fighting it... Ie; not going to happen.
With out a blow off valve or diverter valve, your pressure would backtrack and fight the turbo causing a compressor surge.
Its because there are two guys using a 272 cam with a turbo. a 272 cam has valve overlap to help the 60* motors make more power at the higher rpm, because as we all know no matter what between a 2.8 and 3.4 they both fall flat on thier face after 5500rpm since the intake is so restrictive. BUT they are also using a turbo.
so I was wondering how the motors run at idle with the turbo, thinking that if they dont create any boost at idle would be understandable, because im imagining that if the turbo was making pressure, it would interfere with the idle since the cam has overlap.
My idle speed on the turbo 3.4 with 272 cam is 950-1000 RPM with a Getrag 282 transmission. The boost gauge is mechanical and likely not very accurate. There is some light boost shown at idle but that could easily be a gauge error.
My idle speed on the turbo 3.4 with 272 cam is 950-1000 RPM with a Getrag 282 transmission. The boost gauge is mechanical and likely not very accurate. There is some light boost shown at idle but that could easily be a gauge error.
Nelson
Mechanical gauges are very accurate, but it would have to be a higher quality model... If your boost line was run correctly, without any leaks. Your gauge starts at -30 psi to 30 psi, and is sitting at 0 on idle?
His boost gauge reference line isn't run correctly. He's likely referencing before the throttle plate, where a gauge hovering around 0 would be pretty likely.
So from the last two pages of this thread.. I'm going to invest in a BOV for the best mods to a 3.4l motor lololol sorry just a little humorous sarcasm
Which is not measured or expressed in terms of negative psi.
It was easier to explain, then 0-30 psi vacuum to the left of zero, 0-30 psi boost to the right. Everyone seems to understand it left of zero is negative, but thank you for your correction.
I already answered that, probably somewhere around 10-11 in-Hg. That's inches of Mercury, the standard unit of measurement for vacuum in internal combustion engines. That's what my 3.4 DOHC pulls at least. It won't be the same, but it'll be close.
